Some Geological Phenomena. — Emerso7i. 313 
to be white, which alternated with bands of corresponding 
• width from which the sulphur was absent. 
As one looks down on the bottle from above these rings 
are arranged symmetrically with regard to a median line analo- 
gous to the black band in the optical figure but the two axial 
centers are not placed in the line at right angles to this plane, 
Ijut the two systems of rings sag symmetrically below this line. 
It is clear that this bottle was made by the old fashioned meth- 
od of blowing, that the median plane separating the two sys- 
tems of rings was the plane of junction of the halves of the 
wooden mould in which the clot of glass was blown to the 
shape of the bottle and that the glass chilled quickest along 
this line and became most viscid. The continued blowing then 
caused the glass to flow symmetrically in the two segments 
thus marked out by the lines of flow shown in the figure. 
The flow was not directly outward but outward and down- 
ward, giving the sag in the figure described above, because the 
mould w^as placed on one side during the blowing or because 
one side of the mould was more open than the other. 
As the glass flowed outwardly a rythmical difference of 
surface texture developed and the bands of rougher and 
smoother surface were drawn out into symmetrical rings. This 
difference of surface was brought out by the sulphur which 
was- able to crystallize on only one of the surfaces, probably on 
the rougher one, in which the escape of heat or electricity from 
the irregularities may have favored crystallization. It is an 
illustration of what occurs so frequently in crystals, that 
faces of a given form will be incrustcd and those of another 
avoided by the crystallization of a foreign body. 
2. A } cmarkable Geodc. 
Figure 2. 
Many years ago a missionary graduate sent to the geolog- 
ical museum of Amherst College, a great geode from the 
Orange river in South Africa, which is remarkable for its great 
size, the deep regular pittings like the eyes of a potato and 
rich translucent amber color and firm polish of its surface. 
It was 14 inches long and lo inches high and 93^ thick. I 
hadmanytimes taken a hammer with the intention of learning 
what was in the interior but desisted — the form was so per- 
tVxt. 
